1. Field of the Invention
The present invention relates to an electrical lighting device, and more specifically, to an electrical lighting device utilizing light emitting diodes (LEDs).
2. Description of the Prior Art
Light emitting diodes (LEDs) are frequently selected for large-scale lighting applications, such as traffic lights and other indicator lights. LEDs provide high intensity light with substantially reduced heat generation when compared with incandescent light bulbs. LEDs also consume significantly less power than other sources of light, have a relatively long life and are easily incorporated into digital circuits.
One disadvantage of LEDs is their small size. Typically, LEDs are not readily scalable to larger sizes or higher brightness. In contrast, if greater intensity of light is required in an incandescent application, an incandescent light bulb can be easily exchanged for one having a higher power rating, and consequent physical characteristics, for delivering increased intensity of light. Power ratings and intensities of conventional light bulbs (incandescent, halogen, etc) range from 40W household bulbs to high power bulbs used in spotlights having millions of candlepower, where single LEDs are usually only suitable for smaller applications. To overcome this deficiency of LEDs, conventional practice has been to array a group of LEDs into a single lighting device to achieve increased brightness.
An example of a conventional lighting device incorporating LEDs is shown in FIG. 1. A lighting device 10 comprises a housing 12, a substrate 16, an LED array 18, an optical lens set 22, and a mask 14. The substrate 16 is disposed inside the housing 12. The LED array 18 includes a plurality of LEDs 24 disposed on the substrate 16 for generating red, green, yellow, blue, white or other colored light. A first reflector set 20 comprises a plurality of reflectors 26 installed on the substrate 16 in an array corresponding to the LED array 18. The optical lens set 22 comprises a plurality of lenses 28 installed above the LED array 18 in a corresponding array for focusing light emitted by the LEDs 24 and reflected by the reflectors 26. The light focused by the optical lens set 22 penetrates the mask 14 installed on the housing 12.
Please refer to FIG. 2 illustrating a schematic diagram of light rays emitted by the lighting device 10. A light ray 30 generated by an LED 24 is focused directly by the corresponding lens 28. Each of lenses 28 concentrates light emitted by a corresponding LED 24 and transmits light within a range of angle 34. Finally, the light, focused by the optical lens set 22, penetrates the mask 14 of the lighting device 10.
Due to the structure of the lighting device 10, most of the light focused by the optical lens set 22 penetrates the central part of the mask 14. The remaining light focused by the optical lens set 22 is transmitted to the circumference of the mask 14. Light intensity at the central part of the mask 14 higher than light intensity near the circumference of the mask. Consequently, light emitted by the lighting device 10 is non-uniform in intensity over the surface of the mask.
It is therefore a primary objective of the claimed invention to provide an uncomplicated and inexpensive LED lighting device for providing a more uniform light intensity profile.
Briefly summarized, the claimed invention includes a concave mirror and a convex mirror having a diameter less than a diameter of the concave mirror. The convex mirror is positioned to face the concave mirror and is fixed to the concave mirror. A light emitting diode (LED) array Is fixed to the concave mirror between the concave mirror and the convex mirror. The LED array faces the convex mirror such that light emitted by the LED array reflects off of the convex mirror and onto the concave mirror. A power supply is provided for powering the LED array. Light emitted by the LED array is reflected from the convex mirror onto the concave mirror, and then reflected by the concave mirror to exit the lighting device.
According to an embodiment of the claimed invention, the concave and convex mirrors are parabolic mirrors having metal or plastic bodies coated in metallic reflective material forming reflecting surfaces. The optical axes of the concave and convex mirrors and a central normal axis of the LED array are substantially collinear (or confocal). The LED array is a flat circular array fixed to the metallic reflecting surface of concave mirror. Each LED of the LED array can include a lens for concentrating light onto the convex mirror. Further provided are three stays for attaching the convex mirror to the concave mirror, and a translucent cover spanning the diameter of the concave mirror for protecting the reflecting surfaces of the concave and convex mirrors and the LED array.
It is an advantage of the claimed invention that the concave and convex mirrors can evenly distribute light emitted by the LED array.
It is a further advantage of the claimed invention that light can be delivered to a confined area from an LED array using few components.
These and other objectives of the claimed invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.